Modern well logging systems have called for wider band widths in logging cable for communicating data both to and from a downhole well logging tool to the surface equipment located in a truck. Such fiber optic cables have been in use in surface communication systems for several years and can provide band widths of hundreds of megahertz for the transmission of data in both analog and digital form.
For borehole usage, however, armored logging cables employing multiple electrical conductors have long been in use and equipment in downhole well logging instruments sometimes requires large electrical currents for operation. The electrical conductors in such logging cables have heretofore been abundantly capable of providing both communication paths and power paths from the surface to the downhole instrumentation.
However, the need for band widths on the order of tens of megahertz in order to send digital data from downhole instruments to the surface and vice versa has led to the development of logging cables employing both electrical conductors and fiber optic transmission lines. Since water is the enemy of fiber optics, special means must be employed to hermetically seal the optical fibers used in the well logging environment from the encroachment of water from the borehole and surrounding earth formations. This becomes particularly critical when the logging cable is subjected to the extremely high temperatures and pressures present in a well borehole to a depth of 25,000 feet. In such environments, depending upon mud weight and downhole temperatures, temperatures can reach the vicinity of 400.degree. to 500.degree. F. and pressures reach the vicinity of 20 to 25,000 pounds per square inch.
It is apparent that feeding electrical conductors from the logging cable into the interior of a well logging instrument is a problem which was long ago solved by the industry. However, the feedthrough from a high pressure external environment to a low pressure internal environment in a well logging tool is a new problem limiting the use of fiber optic logging cable in the borehole. A connector which is practical from a field handling perspective is required, especially one which can preserve the integrity of the interior of the well logging instrument from the extremely high pressures and the high temperatures found in well boreholes.